The present invention relates to a voltage controlled oscillator used in a device such as a cellular phone. More particularly, it relates to a voltage controlled oscillator with a power amplifier, and the oscillator contributes to downsizing a device which employs the oscillator as well as increasing the productivity of assembling the device.
FIG. 24 is a block diagram of a conventional cellular phone employing a voltage controlled oscillator. In FIG. 24, the conventional cellular phone comprises the following elements:
(a) antenna 1;
(b) antenna switch 2 coupled to antenna 1;
(c) surface acoustic wave (SAW) filter 3 coupled to a first terminal of switch 2;
(d) demodulator/modulator 5 receiving an output from filter 3, and including a low noise amplifier (LNA) 4;
(e) control circuit 6 coupled to demodulator/modulator 5;
(f) voltage controlled oscillator (VCO) 7 receiving an output from demodulator/modulator 5;
(g) power amplifier 8 receiving an output from VCO 7; and
(h) low pass filter (LPF) 9 coupled between amplifier 8 and a second terminal of switch 2.
An operation of the conventional cellular phone discussed above is described hereinafter. A signal received by antenna 1 travels through SAW filter 3 and is amplified by LNA 4, then demodulated in a demodulating section of demodulator/modulator 5. An output from demodulator/modulator 5 is decoded by control circuit 6, and displayed on a display section (not shown) and supplied as an audio output.
A signal input through a keyboard (not shown) or an audio signal input through a microphone (not shown) is fed into control circuit 6. An output from control circuit 6 is modulated by a modulating section of demodulator/modulator 5. An output from demodulator/modulator 5 is converted into a carrier wave by VCO 7. An output from VCO 7 is amplified by power amplifier 8 and fed into LPF 9, which removes higher-harmonic. An output from LPF 9 travels through switch 2 and is radiated by antenna 1.
Meanwhile, cellular phones have been well accepted by consumers, and thus components to be assembled with ease into a cellular phone are demanded. Switch 2, SAW filter 3 and LPF 9 can be manufactured by low temperature cofired ceramics technique and have been already integrated onto a board. Demodulator/modulator 5 can be also manufactured by silicon-germanium (SiGe) technique, so that it is integrated into one chip IC. Control circuit 6 is also integrated into one chip complementary-metal-oxide-semiconductor (CMOS.)
Device manufacturers can assemble these integrated components into cellular phones with ease; however, VCO 7 and power amplifier 8 are still not integrated yet. Because both the components fall into different fields in terms of engineering and manufacturing, and thus they are difficult to be integrated.
The present invention addresses the problem discussed above and aims to provide a voltage controlled oscillator (VCO) with a power amplifier, the oscillator can contribute to simplifying the assembly of devices including a cellular phone.
The VCO with a power amplifier of the present invention comprises the following elements:
(a) an input terminal for receiving a controlling voltage;
(b) a voltage controlled oscillating section (VCO section) for receiving the controlling voltage fed into the input terminal;
(c) a power amplifier for receiving an output from the VCO section;
(d) a matching circuit for receiving an output from the power amplifier;
(e) an output terminal for receiving an output from the matching circuit;
(f) inspection means for adjusting or inspecting the VCO section and the power amplifier independently;
(g) interference preventive means for preventing interference from the power amplifier to the VCO section;
(h) heat dissipation means for dissipating the heat generated by the power amplifier; and
(i) a board for accommodating those components listed in items (a) through (h).
This structure of the VCO with a power amplifier allows devices including a cellular phone to be assembled with ease.
Another VCO with a power amplifier of the present invention comprises the following elements:
(a) an input terminal for receiving a controlling voltage;
(b) a voltage controlled oscillating section (VCO section) for receiving the controlling voltage fed into the input terminal;
(c) a power amplifier for receiving an output from the VCO section, and a plurality of amplifying circuits are coupled to each other in series; and
(d) an output terminal for receiving an output from the power amplifier.
The VCO section and an amplifying circuit at least on the first stage of the power amplifier include a balance amplifying circuit, and a balance to/from unbalance converting circuit is provided in the power amplifier, which outputs an unbalance signal. The components listed (a) through (d) are accommodated in a multi-layered board which allows surface mounting.
This structure allows the VCO with a power amplifier to be mounted as it is to the devices including a cellular phone, thus the devices can be manufactured with ease. The power amplifying circuit on the final stage in the power amplifier outputs an unbalance signal, so that a balance to/from unbalance converting circuit needs not to be coupled separately to the output of the power amplifier. Thus there is no power loss due to the balance to/from unbalance converting circuit, and power can be saved.